The present invention can be applied in any firearm having a sear moved between a stop-fire position, in which a discharge mechanism of the firearm is held by the sear tip against movement that would result in firing of a round, and a fire position, in which the discharge mechanism is released by the sear tip to permit movement of the discharge mechanism to fire a round. In the detailed embodiment shown, the present invention finds particular application in rifles in which the sear of a rifle engages a sear notch on the operating rod (op rod) to hold back the op rod until sufficient pressure is applied to the rifle's trigger to release the op rod and permit its cycling. These rifles include those that operate only in semi-automatic mode, those that operate in fully-automatic mode, and those that have the ability to be selectively switched from semi-automatic to fully automatic mode. In semi-automatic mode, the sear returns to its stop-fire position to again hold the op rod after the firing of a single round, and a trigger mechanism must be actuated to fire another round. In fully automatic mode, the sear remains out of a stop-fire position as long as the trigger mechanism remains actuated, and the sear only returns to its catch position upon release of the trigger. It has been found that the return of the sear can be too quick in some instances, presenting room for improvement of the return mechanics.
In all of these rifles, the sear tip often rubs against a length of the op rod before engaging with the sear notch. This can cause undesirable wear to the sear tip and the op rod. Any appreciable decrease in the length of the rub between the sear tip and op rod during a firing cycle will reduce wear.
Some rifles are provided with select fire assemblies that permit the rifle to be operated to be either fully automatic or semi-automatic. General examples are found in U.S. Pat. Nos. 8,453,554 and 8,459,172, which specifically address M60 and M249 rifles. One aspect of these rifles is that they have op rods with two sear notches, a primary sear notch and a safety sear notch. The safety sear notch is provided in many fully automatic rifles in order to avoid runaway in the instance of ammunition not driving the op rod back far enough, whether due to weak/faulty ammunition or a fouled gas tube or op rod, either of which can prevent the op rod from being driven back far enough during a firing cycle to engage the primary sear notch with the sear. The safety notch is placed so that the sear can engage it even though the op rod is not forced back as far as it should be under normal, proper operation. It has been found that, when in semi-automatic firing mode, the sear can return to the stop-fire position from the fire position so quickly that it will engage the rearward sear notch and stop the op rod before the firing of a round. This prevents the successful implementation of such select fire trigger assemblies (and similarly functioning apparatus) in rifles having op rods with two sear notches. This problem specifically led to the development of the present invention, but the invention, again, can be implemented in any desired firearm where it is believed benefits could be derived from a delay in the sear return.
Thus, there is a need in the art for delaying the return of a sear to its notch-engaging or stop-fire position.